Video Transcript
In the circuit below, what will
happen to the potential difference across the lamp filament when connecting a
resistor in parallel with it? (A) It will stay the same. (B) It cannot be determined without
knowing the resistance values of the lamp and the resistor. (C) It will increase. (D) It will decrease.
In this question, we’re shown this
diagram. Currently, the circuit diagram
consists of a cell and a lamp filament. If the cell provides a potential
difference of 𝑉, then the potential difference across the lamp filament will also
be 𝑉. Now we will add a resistor in
parallel with the lamp filament to see how the potential difference across the lamp
filament changes. So we now have a parallel
circuit. The path between the two terminals
of the cell splits into two paths at point 𝐴. The paths then join together again at
point 𝐵. The cell will still provide a
potential difference of 𝑉 to the circuit, as the cell did not change in emf.
Let’s recall that the potential
difference across each path of a parallel circuit is the same. No matter what the resistance
values of the components along the parallel paths are, the potential difference
across each will be the same. And in this case, that potential
difference will be equal to 𝑉, the potential difference of the cell. That is, the potential difference
across the resistor is 𝑉, and the potential difference across the lamp filament is
also equal to 𝑉, the same as it was before adding the resistor in parallel.
Therefore, when adding a resistor
in parallel with a lamp filament, the potential difference across the lamp filament
will remain the same. So, option (A) is the correct
answer; it will stay the same.
